Computer tomography (CT) imaging is a relatively recent development that has captivated the interest of those involved in imaging technology. CT has been most accepted and adopted as standard procedure in the medical field, since it provides a more detailed analysis of internal body parts that do conventional X-rays, it offers more control for setting variables according to the particular focus of the image, and is less costly since the results are immediately computerized, thereby eliminating the time delay and cost involved in the development of X-ray negatives. As a result, leading manufacturers of equipment incorporating CT technology have emerged, such as General Electric's Medical System's Division and Siemens, AG. In addition, numerous smaller companies are now manufacturing CT equipment in this developing and competitive field.
CT equipment consists of apparatus largely incorporating that of conventional X-ray systems, consisting of basis components such as a radiation source for positioning above the subject and a receptor negative plate positioned beneath the subject (FIG. 20). The data generated at the receptor is analyzed using various possible methods known in the field to reconstruct the image of the area targeted on the subject. At the heart of CT equipment is the controller, being a computer with specialized software for controlling the overall operation, including the processing of the generated data.
Some advances in this field fall short of achieving the desired clarity of a reconstructed image. For example, the patent to Katsevich, U.S. Pat. No. 5,550,892, describes a method for determining the location and value of a discontinuity between a first internal density of an object and a second density of a region within the object. However, only relative attenuation data of the radiation beam is determined and used. While this is helpful in enhancing the local tomographic image, the method does not actually reconstruct the image. Its use of LAMBDA as the local tomography function is an algorithm for taking the measurements of the relative attenuation data and manipulating the measurements via the algorithm for determining the location of the discontinuity.
Along with the acceptance of CT into the mainstream of the medical and other fields as well, has emerged the health concern about the radiation dosage it imposes onto the human body and the potential harmful effects of that exposure. Two opposing factors immediately come into play with the use of CT: (1) high resolution and improved detailed imaging is obtainable with CT that has not been achieved before. However, (2) to achieve these desired results that help immensely in making a proper diagnosis and evaluation, a larger dose of radiation is focused onto the subject with CT technology that is used in other types of imaging methods, such as conventional X-ray negative imprints. The main problem with CT, therefore, has been the potential danger it represents due to excessive radiation exposure, and the technology has been grappling with the delimina of how to maintain the superior diagnosis output of CT while keeping the radiation exposure in control to ensure its safety to the patient, or its user in any non-medical application.
Conventional tomography is a global procedure in that the standard convolution formulas for reconstruction of the density at a single point require the line integral data over all lines within some planar cross-section containing the point. A desirable goal has been to reduce radiation exposure for safety purposes while maintaining high quality image output, although this has heretofore not been achieved to a satisfactory level. While developments in CT imaging have made marked improvements in its technological capabilities, the problem as to the radiation effects has not received the same degree of attention and has remained an unsolved concern in the use of computer tomography.